Nonreciprocal wave transmission components



Aug. 27, 1963 H. SEIDEL NONRECIPROCAL WAVE TRANSMISSION COMPONENTS Filed Jan. 11, 1961 2 Sheets-Sheet 1 FIG.

GVROMAGNET/C MATERIAL GVROMAG/VET/C f MATERIAL FIG. 4

I a" 2 FIG. 7

FIG. 8 GVROMAGNET/C E I x x 0 MATERIAL e INVENTOR H. SE/DEL ATTORNEY H. SEIDEL NONRECIPROCAL wgwE TRANSMISSION COMPONENTS.

2 Sheets-Sheet 2 Filed Jan. 11, 1961 FIG. .9

GYROMA GNE T/C MA TERM L FIG. /0

I03 [0/ GVROMAG NE T/C MA TER/AL INVENTOR H. 55 /DE L ATTORNEY 3,102,244 NONRECIPROCAL WAVE TRANSMISSION COMPONENTS I Harold Sendel, Fanwood, NJ .,assignor to Bell Telephone Laboratories, Incorprated,'N ew York, N.Y., a cor- I poration of New York Filed Jan. 11, 1961, Ser. No. 82,090

20 Claims. (Cl. 333-241) This invention relates to electromagnetic wave transmission systems and more particularly to directional or non-,

reciprocal attenuators and phase shifters for use in such systems. Whereas special emphasis is devoted to twoelement transmission systems operating in'the TEM mode, the invention can readily be practiced using hollow, conductively bounded, waveguides or other types of transmission media.

This application is a continuation-impart of my copending applications Serial No. 777,924, filed December 3, 1958, now abandoned, and Serial No. 858,244, filed December 8, 1959, now abandoned.

The use of materials having gyromagnetic properties to obtain both reciprocal and nonreciprocal efiects in microwave transmission circuits is widely known in the art. These materials have found numerous and varied applica- United States Patent 0 tions in propagation structures employing waveguide components, and are therefore limited in their operation to the microwiave frequency range and above. A rsum of the early work done using waveguide elements is contained i n technical papers too numerous to mention. The need for nonreciprocal circuitelements, however, is at least as great in the lower frequencyrang'es in which twoline transmission components operating in the TEM mode are used. These lower frequency ranges include the ranges designated as very high" frequency and ultra high frequency. f m

' It is, therefore, the broad object of this invention to produce nonreciprocal transmission effects in in transmission systems operating in the TEM mode.

In United States Patents 2,895,114 and 2,892,160, issued to J. l-I. Rowen on luly 14, 1959 and'lune 23, 1959, respectively, and in United States Patent 2,892,161, issued to 1. M. Clogston on June 23, 1959, there are disclosed structures and techniques for utilizing one ormore of the several'nonrecipro'cal effects produced by polarized elements of gyromagnetic material at frequencies of wave energy below a few thousand megacycles. tures comprise two branch coaxial or balanced transmission line networks capable of introducing a nonreciprocal attenuation or nonreciprocal phase shift to wave energy in the frequency range in which coaxial and balanced transmission lines are used. 1 1

, Like their microwave counterparts, the lower frequency isolaters and nonreciprocal phase shifters described in the above-mentioned patents operate by exciting in an element of polarized gyromagnetic material a circularly polarized component of radio frequency magnetic field that'rotates in one sense relative to the steady polarizing field when the radio frequency wave is propagating in one direction, but in the opposite sense when the wave is propagating in the opposite direction. When thepolarizing field is adjusted to the strength necessary to produce gyromagnetic resonance in the gyromagnetic material, a substantial part of theenergy is absorbed for one direction of rotation and direction of propagation, butit is substantially unaffected for the other direction of rotation and direction of pro pagation. When the polarized field is adjusted to a strength substantially below that necessary to produce gyromagnetic resonance, a nonreciprocal phase shift is produced. The prior art devices, however, tend to be large and relatively complicated in their structure, and

These structhe crossover point.

Patented Aug. 27, 1963 require a fairly large piece ofgyroma'guetic material. ELIF'LhEIIHOIB, they are, in general, nontunable.

It is therefore a more specific object of this invention to simplify the means for generating circularly polarized radio frequency magnetic fields whose sense of rotation is a function of the direction of the wave propagation.

In accordance with the invention, an element ofgyromagnetic material is simultaneously coupled to two'electrically spaced regions of a transmission system. The delayed portion of'the propagating signal is fed back, and coupled to, a small element of gyromagnetic material so as to induce a magnetic field component at an angle to that induced by the other coupled region. ing the electrical delay and the spatial phase angle of the intersecting fields a circularly polarized resultant radio frequency magnetic field is produced in the gyron'i agnetic material whose sense of rotation is opposite directions of propagation of the wave energy. Depending upon the degree of coupling to the gyromagnetic material, low-loss nonrec-iprocal phase shift or nonreciprocal attenuation effects are obtained. A steady biasing field is directed normal to the two radiofrequency magnetic vectors and is adjusted to produce gyromagnetic resonance in the ma terial.

It is a feature of the invention that the nonreciprocal device so produced is readily tunable with frequency merely by changing the spatial phase angle at which the radio frequency magnetic fields intersect in the gyrom'agnetic material, and by adjusting the magnetic biasing field intensity. These adjustments may be gauged and made simultaneously as the frequency is varied..

It is a further feature of the invention that the element of gyromagnetic material used is extremely small, as'is the entire structure. In a first principal embodiment of the invention, nonreciprocal efiects are obtained in a two-wire transmission system by bending at least one of the wires back upon itself to form a loop. The electrical length of the loop and the spatial angle at which the wire crosses itself are ad justed to produce a circularly polarized magnetic field at A magnetically polarized element of gyromagnetic material is located in the region of the circularly polarized high frequency magnetic field to produce nonreciprocal transmission eifects. I

In the above-described illustrative embodiment the magnetic fields that build up within the loop structure are essentially only those of a unidirectional traveling Wave. As a consequence, -a relatively small magnetic field density is developed resulting in a correspondingly small interaction between the gyromagnetic material and the electromagnetic wave energy associated with the propagating wave. One way of increasing the energy interaction between the traveling wave and the gyromagnetic material is to increase the size of the material, thereby extending the region over which the wave and material can interact. This technique has been used before with the obvious disadvantages that large pieces of material are needed and the dielectric losses are substantially increased. On the other hand, the same effect can be produced by causing the wave to traverse a small gyromagnetic element many times. This latter result can be readily produced by coupling the small element of gyromagnetic material to a resonant section of transmission line wherein successive reflections from theline ends produced the efiect of multiple passes.

Waveguidecavities which operate between electric walls are well documented and understood. It isequally feasible, however, to form a cavity by housing a length of transmission line between two magnetic walls (that is, open ends). In the ease of an electric wall cavity, coupling is accomplished by opening up small holes in the short circuit wall. Similarly, in the open circuit cavity, coupling By properly relatof the input and output transmission lines to the cavity structure is accomplished by placing said lines in close proximity to the cavity ends. A typical form of coaxial line cavity then, is one in which a nominally half-wave center conductor is coupled by fringing fields to gapspaced transmission lines at either end. For all practical purposes, if the gaps are relatively small they may be represented as small series capacitors over the frequency band of operation.

Applying the technique of multiple reflections, improved nonreciprocal two-element transmission components are produced, in accordance with the invention, by coupling an element of igyromagnetic material to two series-connected sections of transmission line, such as a pair of coaxial cavities, crossed in the region of their cur-rent maximum points.

In a second principal illustrative embodiment of the invention, the coaxial cavities are crossed at right angles and the output of the first cavity is delayed a quarterwave before being coupled to the input of the second cavity. The entire structure is observed to take on the form of a loop in which the time and spatial phase angles of the intersecting magnetic field components are such as to produce a circularly polarized resultant radio frequency magnetic field in the gyromagnetic material whose sense of rotation is opposite for opposite directions of propagation of the Wave energy. It the coupling between the gyromagnetic material and the resonant cavities is in the region of critical coupling or below, nonreciprocal attenuation eifects are produced. At couplings greater than critical coupling, the lossy eifect is diminished and the primary effect is that of nonreciprocal phase shift.

The use of resonantly tuned cavities greatly enhances the interaction between the gyromagnetic material and the propagating electromagnetic wave energy by producing, in effect, a substantially greater magnetic field intensity in the region of the gyromagnetic material. As a result, the attenuation or phase shift produced is much greater for a given volume of gyromagnetic material.

In one configuration of the second principal embodiment of the invention, the ninety degree phase delay is obtained by inserting an appropriate length of transmission line between the output of the first cavity and the input of the second cavity. However, as is known in the filter art, two large series reactances separated by a quarter wavelength can be recomposed into a single larger react-ance substantially equal to the product of the two reactances divorced of any spacing whatsoever.

Accordingly, in an alternative configuration of the invention, the required time delay is produced by adjusting the amplitude of the coupling between the output of the first cavity and the input of the second cavity. This results in a nonreciprocal coaxial component of greater simplicity and compactness of design.

While, as indicated above, special emphasis has been placed upon coaxial, or two-wire, transmission systems, this in no way was intended to restrict the application of the principles of the invention to such systems. To the contrary, the principles of the invention can be readily practiced using hollow, conductively bounded waveguides or other transmission media.

These and other objects and advantages, the nature of the present invention, and its various features, will appear more fully upon consideration of the various illustrative embodiments now to be described in detail in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of the first principal embodiment of the invention showing a coaxial nonreciprocal device;

FIG. 2. is a close-up view of the crossover region showing the magnetic fields in the region of the gyromaignetic material;

FIG. 3 shows, by way of illustration, the space orientation of the magnetic field vectors in the region of the gyromagnetic material;

FIG. 4 is a time vector diagram of the radio frequency magnetic fields in the region of the gyromagnetic material;

FIG. 5 shows an alternative arrangement of the first principal embodiment of the invention using parallel wire transmission lines;

FIG. 6 is a perspecitve view of the second principal embodiment of the invention employing resonant sections of coaxial line;

FIG. 7 is a block diagram equivalent of the delay network;

FIG. 8 is an alternative block diagram representation of the delay network;

FIG. 9 shows an alternative arrangement of the second principal embodiment of the invention; and

FIG. 10 illustrates the application of the principles of the invention to other transmission media.

Referring more particularly to FIG. 1, a perspective view of the first principal illustrative embodiment of the present invention is shown connected and utilized to produce nonreciprocal transmission effects. Such a device comprises the two intersecting channels 10 and 11 which, for convenience, may be integrally constructed by milling or casting them in a block 13 having a suitable cover plate 14. Channels 10 and 11 are connected to each other within block 13 by means of an additional channel 12 and thus form a continuous channel from the input of channel 10 to the output of channel 11.

Suitably supported within channels 10, 11 and 12 and extending longitudinally therein in a plane parallel to the walls of said channels is the conductive member 15. Together, member 15 and the walls of the several channels, serving as the conductive ground plane therefor, form a strip-line or coaxial wave supporting structure. It will be noted that in conforming to the channel boundaries, conductor 15 bends back upon itself in a plane essentially parallel to the ground planes to form a loop 16 which extends from a point a on conductor 15 to a point b on conductor 15. From the crossover point defined by the axis ab normal to the plane of loop 16, the transmission line continues in both directions away from loop 16 and connects to the rest of the transmission system. As shown, the input signal is supplied from a source to member 15 in channel 10, whereas the output connects to that portion of member 15 in channel 1 1.

Located between the two adjacent ends of loop 16 along the axis ab is an element of gyromagnetic material 20. The term gyromagnet-ic material is employed here in its accepted sense as designating the class of magnetically polarizable materials having unpaired spin systems involving portions of the atoms thereof that are capable of being aligned by an external magnetic polarizing field and which exhibit a precessional motion at .a frequency within the range contemplated by the invention under the combined influence of said polarizing field and an orthogonally directed varying magnetic field component. This precessional motion is characterized as having an angular momentum, a gyroscopic moment and a magnetic moment. Typical of such materials are ionized gases, paramagnetic materials and ferromagnetic materials, the latter including the spinels such as magnesium aluminum ferrite, aluminum zinc ferrite and the rare earth iron oxides having a garnet-like structure of the formula A B O where O is oxygen, A is at least one element selected from the group consisting of yttrium and the rare earths having an atomic number between 62 and 71 inclusive, and B is iron optionally containing at least one element selected from the group consisting of gallium, aluminum, scandium, indium and chromium. In the particular embodiment of the invention shown in FIG. 1, aluminum-substituted yttrium iron oxide is used.

The element of gyromagnetic material 20, in the illustrative embodiment of FIG. 1, is in the shape of a disk, disposed with its faces normal to axis ab. Element 20, however, may assume any other convenient shape since the particular shape is not essential to the opera tion of p the invention. A static magnetic field H is applied.

parallel to axis ab (normal to the faces of the disk) and is adjusted as will be explained in greater detail hereinafter.

means (not shown) such as an electric solenoid, a permanent magnetic structure or in some instances the disk 20 itself may be permanently'magnetized. 7

To produce isolator action, conditions must be lished whereby energy can be dissipated in one direction of transmission to a substantially. smaller degree than in the reverse direction of transmission.

nomenon of 'gyromagnetic resonance is utilized to provide thefnecessary lossmechanism. As is well known,

magnetically polarized gyromagnetic materials exhibit Y distinctly .dilferent properties depending upon the nature "of the applied magnetic fields. These unusual properties which are produced can be explained b y recognizing that i the Igyromagnetic materials contain unpaired electron or nuclear spins which tend to align themselves with the polarizing fieldflbut which can be made to precess about an axis parallelt-o thefdirection ofthis fieldby the application of a bighfrequency magnetic field. The magnetic moments associated with the spinning atomic particles,

howeven tendto precessin onlyone angular sense and resist rotation in "the; opposite sense. .It is therefore evident that oppositely circularly polarized waves influence the gyromagnetic material ditferently, depending upon their sense of rotation. This is so since a circularly polarized wave; rotating in one direction will be rotating in the easy angular direction of precession of the magnetic moments whereas an oppositely rotating circular polarized wave will betotating in a sense inconsistent with the natural behavior of the magnetic moments of the momagnetic material. As a consequence, when thehighfrequency magnetic field i rotating in the same sense as the preferred direction-of precession of the magnetic moments, it couples strongly to the gyromagneticmaterial. However, very little coupling takes place between the external magnetic field and the magnetic moments 1 when the high-frequency magnetic field is rotating in the opposite angular direction. I

. While this difference in coupling, and consequent difference in permeability provided by oppositely rotating circularly polanizedmagnetic fields is not limited to any particular frequency or polarizing field strength, particula-rlyuseful effects are observed at gyromagnetic resonance 1 'when the frequency of the circularly polarized magnetic field is the sameas the natural precessional frequency of the magnetic moments as determined by the strength of the polarizing fields Under these patricular conditions, a large amount of power can be extracted from, a

magnetic field circularly polarized inthe preferred sense and absorbed in the gyromagnetic "material. However,

very littlepower is absorbed fro-man oppositely circularly polarized component. i

The biasing field l-I may be supplied by any suitable In the isolators constructed in accordance with the invention, the phenormal tothe p'laneof loop to both field components f and f The spatial orientation of the variousmagnetic fields in the region of the gyromagnetic material is shown in the space vector diagram or FIG. 3.

Because of the time delay experienced by the wave enr.v

ergy in -traveling frompoint a to point b along conductor 15, there is a corresponding time delay associated with the fields f,, and f in particular, if at a particular op-, erating frequency the loop 16 is made to be a quarter of .a wavelength in length between points q and b, field f lags field f by ninety degrees, as shown in the/time vector diagram of FIG. 4. Because of ninety degree time diiference, as field f passes through its maximum amplitude and starts to decrease towards zero,field f is passing through zero and is'star-ting to increase towards its maximum value. The efiect of having the field com- ,ponents f and 5, varying in thismanner, is to produce the equivalent of a single resultant field vector which appears-to rotate in space in the region of the gyromagnetic material 20. With the polarizing field H directed nor:

trial to the plane of field components f and f as shown in FIG. 3, a negative or counterclockwise notationis produced when viewed along the direction of the biasing field,- This sense of circularly polarizing magneticfield,

however, is opposite to the natural pre'cessional'sense of the magnetic moments in the gyromagnetic material and, little or no interaction takes place between the electrical energy and-the; gy'romagnetic material and substantially; all the wave energy introduced into the system in the for in the relative time phase relationship between the magnetic field vectors such thatthe phase of 1",, lags 7",, by

ninety degrees, as-shown in FIG. 4. As a consequence,

the resultant field produced by v and f appears to rotate in a positive or clockwise sense as viewed along the direction of the biasing field H This sense of ro-. tation is the same as the preferredsenseof precession of the magnetic moments in the gyromag netic material and hence energy is absorbed from the circuit and dissipated in the gyromagnetic material. 1 v

y 'In an alternative embodiment oft-he" invention, a pair of loops are'insertedin the two elements of; a parallel wire transmission line. Referring more particularly to FIG. .5, anillustrative embodiment of a parallel line type It is apparent, therefore, that a cir-cularly polarized magnetic field must be generated whose sense of rotation is dependent upon the direction of propagation of the signalthrough the system. I

FIG. 2, given for the purposes of explanation, shows diagrammatically the component magnetiefieldpatterns in the region of the crossover point.

magnetic fields in the vicinity of conductor. .15 are i-llus- In particular, the

trated by the closed loops f and f representing magnetic v, field components having substantiallyequal amplitudes nonreciprocal device constructed in accordance with the pr1nc1ples of the invention is shown,c omprising-a pair of 7 parallel elongated conductiveelements 51 and 52. Each of the elements-51 and 52 have at least one loop 53 and 54, respectively, included along their lengths. At the re-;

spective crossover points there are located disks of gyromagnetic material 55 and 56. Each disk is magnetically biased by an external biasing field H applied in a direcencircling conductor'15 at points a and b, respectively.

The planes of the respective loops are normal to the longitudinal axis of conductor 15. Since the two ends of loop 16 formed by conductor :15 are normal to each other,

the magnetic field components f,, and i are likewise normal to each other in the region of disk 20'. The

magnetizing field H also shown, is direetedsubstantially tion normal to the-planeof loops 53 and 54.

In theparticular embodiment of the invention shown in FIG. 1, circular polarization wasinduced inf the: gyromagnetic material by making both ."the time phase and the space phase of the exciting field components ninety degrees. It should be noted, however, thatthere are other combinations of time andfspac'e phasings which also pro duce a 'cincularly,polarized resultant field. It can be shown that, in general, for any arbitrary space orientation,

( ot the two equal field components (where a is assumed to be positive angle) there is a relative time phase, ,8, thatproduces circular polarization where 16, consequently normal where n is a whole number. Thus, if in the embodiment of FIG; loops 53 and 54 have an electrical length other than a quarter wavelength, the angle a at the crossover points may be adjusted to an appropriate angle in accordance with the above-mentioned relationship. Furthermore, if the angle a is made adjustable, the device may be tuned as a function of frequency. Thus, for example, as the frequency is changed and the electrical lengths of the loops 53 and 54 correspondingly change, circular polarization may nevertheless be induced in the gyromagnetic material by appropriately varying the crossover angle a.

In the description relating to the embodiment of FIG. 1, the device was referred to as an isolator. In my copending application Serial No. 774,389, filed November 17, 1958, now Patent No. 3,010,085, an equivalent network for the gy'romagnetic material was given, and it was shown that whether or not energy is absorbed in the gyromagnetic material depended upon the degree of coupling between the system and the gyromagnetic material. In particular, it was there shown that optimum isolator action is obtained for the range of coupling about critical coupling. It can similarly be shown that for tight coupling a low-loss nonreciprocal phase shifter is essentially obtained rather than a nonreciprocal attenuator. Thus, depending upon the degree of coupling, it is possible to obtain either nonreciprocal attenuation or nonreciprocal phase shift.

In the first principal embodiment of the invention described above, the high-frequency magnetic fields in the crossover region are those associated with a unidirectional traveling wave. As was also indicated above, the resulting interaction between the gyromagnetic material and the propagating wave energy is relatively small. In the second principal embodiment of the invention to be described hereinafter, this interaction is substantially increased by resonating the transmission line in the crossover region. Such an arrangement is illustrated in FIG. 6.

The device of 'FIG. 6 comprises a conductive block 60 into which there is milled the two intersecting channels 61 and 62. Channels 61 and 62 are connected to each other within block 60 by means of an additional channel 63, thus forming a continuous pathway from the input to channel 61, to the output of channel 62.

Suitably supported within channels 61, 62 and 63 by the low-loss dielectric material 64, and extending longitudinally therein parallel to the several walls of said channels, are the conductive members 65, 66 and 67. Each member is physically separated from each adjacent member by a given distance d so as to form a conductive gap therebetween. Together members 65, 66 and 67, in conjunction with the walls of the several channels (including cover plate 68) which serve as the conductive ground plane therefor, form a stripline or coaxial wave supporting structure. Electromagnetic wave energy is coupled into and out of the structure by means of members 73 and 74, which are similarly separated from the ends of members '65 and 67, respectively.

It will be noted that in conforming to the channel boundaries, the center conductor of the transmission line comprising members 65, 66 and 67 bends back upon itself in a plane essentially parallel to the ground planes to form a loop which extends from a point a on conductor 65 to a point b on conductor 67 and includes member 66 therebetween. From the crossover point defined by the axis ab normal to the plane of the loop, the transmission line continues in both directions away from the loop and connects to the rest of the transmission system. As shown in FIG. 6, the input signal, indicated by the arrow 69, is supplied from a source to member 65 in channel 6 1, while the output, indicated by the arrow 70', is coupled to member 67 in channel '62. The element of gyromagnetic material Z1, in the illustrative embodiment of FIG. 6, is in the shape of a disk, disposed with its faces normal to axis ab. Element 71, however, may

assume any other convenient shape since the particular shape is not essential to the operation of the invention. A static magnetic field H is applied parallel to axis ab (normal to the faces of the disk) and is adjusted as was expalined in connection with FIG 1.

The biasing'field H may be supplied by any suitable means (not shown) such as an electric solenoid, a permanent magnetic structure, or in some instances the disk 71 itself may be permanently magnetized. Thus, in its basic aspects, the structure of FIG. 6 is similar to that of FIG. 1.

In the preceding description of the operation of the nonreciprocal attenuator of FIG. 1, it was explained how the radio frequency magnetic field interacts with the gyromagnetic material and how, under certain conditions, energy is transferred from the signal to the gyromagnetic element and dissipated therein. Let us now consider the amount of energy thus dissipated. It can be shown that the energy absorbed in the gyromagnetic element is a function of the susceptance of the gyromagnetic material, a", and the intensity of the high-frequency magnetic field H Specifically the absorbed power P is proportional to the product of a" and the square of the field strength,

ab I r f where a is a constant.

It is apparent from this relationship that by increasing the value of H the attenuation of the isolator in the reverse, or lossy direction can be substantially increased.

In accordance with the invention, the radio frequency magnetic field components in the region of the gyromagnetic element 71 are maximized by resonating the conductive members 65 and 67 and crossing them in the region of their current maxima. Accordingly, the length l \of conductor 65 and the length l of conductor 67 are adjusted to be approximately an integral number of half wavelengths at the frequency to be attenuated. As is well known, the current distribution along .an open-ended resonant cavity is essentially sinusoidal, being a minimum at the ends, and a maximum at odd multiples of a quarter wavelength from the ends. Accordingly, for maximum interaction conductive members 65 and 67 are made to cross each other at points along their lengths that are odd multiples of a quarter wavelength from their respective ends, thus maximizing the radio frequency magnetic field to which the gyromagnetic material is subjected.

For the case where both I and l are approximately equal to half a wavelength, conductive members 65 and 67 are crossed at their midpoints. This particular location is not to be regarded as a limitation, however. Thus, Where less than maximum interaction is preferred in some specific application, the crossover region (and the location of the gyromagnetic material) may be shifted to some other point along the resonant sections of line. Obviously, a large range of interactions may be realized by varying the position of the crossover region.

In the description of the embodiment of FIG. 6 the cavity lengths l and l' were characterized as approximately equal to half a wavelength, or whole multiples thereof. However, a modification of the cavity length over its nominal half wavelength value must be made to take into account the series reactance introduced by the coupling gaps adjacent to each end of the resonant line. The correction to the length for each gap is given by the formula where 'y is in electrical degrees and X is the gap reactance. Applying the correction twice to take into account both gaps, the electrical length 0 of the coaxial cavity is given by work (member 66') is given by terial 94 inserted-therebetween. f

where n is an integer, and X and X2 are the series reactances introduced by the-conductive gaps between the cavity and its adjacent members. In the embodiment of FIG. 6, where the gap lengths, 'd, are equal The overall Q of the two cavities is that of a quarter wave coupled resonant pair and is given as The bandwidth of ca ch stri Cavity is related to its loadfid Qwhichisgivenby i p 1 The electrical length (p of the quarter wave delay net-o j where m is an integer.

p In the embodiment of the invention shown inFIG. 6 and herein described, thecavities have. been oriented so (2m arotan that the rnagnetic field componentsintersect :atright angles, and the time delay was adjusted to be ninety de The spacing between the tuned segments 90 and 91 and conductor 92 produces a series reactance X between each of the resonant sections and the transmission line. Accordingly, the spacing between section90 and section 91 is adjusted toproduce a series reactance substantially equal to X So adjusted, the circuit of 'FIG. 9 has exactly the same electrical properties as the circuit of FIG. 6, and may be utilized in precisely the same man ner. Thus, a resonantly biased element of gyromagnetic material 95 placed between the cavities in the crossover region will produce nonreciprocal transmission eifects in the manner explained hereinbefore.

So far we have only considered two-wire or coaxial line transmission systems. However, as waspreviously indicated, the techniques described abovemay be readily applied to other transmission media. One'simple illustration of this application is given in FIG. 10 where a hollow, conductively'bounded rectangularwaveguide 100 is caused to bend backv upon itself to formthe familiar loop structure. An, aperture 101 extending'ithrough the contiguouswide walls 102 and 103 in the crossover reg-ion will expose magnetic field components having particular spatial and time phase diiferences. By adjusting these phase differences in accordance with Equation 9, a region of circular polarization maybe established; Nonreciprocal effects can then be obtained by'inserting a'suitably magnetized element of gyrornagnetic material grees. However, as waspointed out above, circular po.-y

larization of the radio ,frequency magnetic field may be obtained by causing the magneticfield components to intersect at some angle a other thannincty degrees, provided the time phase delay, [3, is adjusted such that It turns out, however, that for the special case where a andfl tare bothequail to ninety degrees, the maximally fiat bandpass characteristic is obtained. A nonrcciprocal if device so constructed is then notallimite-d'by the loaded Q of either resonator, but rather by thefline width of the gyromagnetic material alone.

Some simplification of the embodiment of FIG. 6 can be obtained by. modifying the network used to obtain the ninety jdegreephase-delay betweenthe signal field corn ponents f, and 1%,. In 1 16.? there is shown the equivalent circuit of the delay network which co mprises con- 1ti4'throughaperture 101. The operation of the SlZIllC-f ture ofFIG. '10 is, in all respects, substantially as described above.

In all cases it is understood that the above-described arrangements are illustrative of but 'a small number of the many possible specific embodiments which can represent. applications of the principles of the. invention.

'For example, Whereas the embodiment of FIG. 9 is shown comprising a section of unbalanced strip-line, the

invention can be practliced'in principle using balanced strip-line, coaxial cable or two-wire transmission line. Similarly the waveguide in FIG. '10 may be resonated in the crossover region. Thus, numerous and varied other arrangements can readily be devised in accordance with 7 these principles by those skilled in the art without departe ing from the spirit and scope of the invention.

-What is claimed is: ,l l. A nonreoiprocal wave transmission component comprising atwo-conductor transmission line, at least one of said conductors forming a loop of electrical length 6,

said one conductor crossing-itself at an angle a, such that ductive member '66 and its two adjacent gaps, The network comprises the two series-reactances X tand'Xg produced by the gaps between"member -'66 and the adjacent members 65 and 6 7, and the ninety degree reciprocal phase shift produced by member 66. r

actances separated by a quarter wavelength-can be reto the product of the two reactancesdivorced of any spacing whatsoever, The" alternate filter structure,

shown in FIG. 8, is usually described as a directcou'ple filter as opposed to the quarter wave filter of FIG. 7;

design. The isolator of FIG. 9 comprises the two crossed resonantly tuned sections 90 andf91 inser-ted;in" one branch '92 of the two element transmission paths comductively insulated from the tuned sections 90 and 91 and conductor 92 by a sheet of low-loss dielectric inasaid members when energized having a field pattern inprising conductors 92 and 93; Conductor 93 is conoc'=(2n|1)1r,8, n being an integer, an element of magnetically polarizable material exhibiting gyromagnetic effects over the operating frequency range of said com ponent located between opposite ends of said loop at said crossover point, and means for biasing said element in, a

direction substantially normal to the plane of said loop.

2. Tlhe combination according to claim 1 wherein the electrical length of said loop is a quarter wavelength of a frequency within said operating range and said opposite I I ends of said loop formed by said one I .60 composed into a smgle large reactance substantlally equal each other atan angle of ninetydegrees. I

3. The combination according toclann 1- wherein one ofsaid conductors surrounds the other of said conductors. 4. In an electromagnetic wave transmission system supportive of a range of operating frequencies, means for selectively attenuating a band of frequencies within said range comprising a pair of parallel elongated conductive members, means for energizing said members,

eluding loopsof magnetic field, at least one of said members being bent back and crossing over itself at-an angle.

on to form a'loop of electrical length a at a "frequency within said band such that or and [3 satisfy the relation ship a=(2n+ 1)1r-B, wherein n is an integer, an element of magnetically polarizable material capable of exhibitinggyromagnetic effects over said range of operating conductor cross 1 1 frequencies located at the crossover point, means for magnetically polarizing said element, means for varying said band of frequencies and means for varying the crossover angle a as said electrical loop length ,8 varies to maintain said relationship between a and ,B.

5. A nonreciprocal electromagnetic wave device supportive of wave energy in the TEM transmission mode comprising a section of two-conductor transmission line having an input end and an output end, means for applying wave energy at a given frequency to the input end of said line, said wave energy propagating from said input end toward said output end past first and second successive portions of said line having a time phase difference B therebetween, an element of material capable of exhibiting gyromagnetic effects at said given frequency located in a region proximate to said line, means coupling Wave energy exclusively between said two distinct portions of said line and said element, said coupling means being supportive of magnetic field components with the wave energy at the first of said portions inducing first magnetic field components in said region predominantly of a single polarization and with the wave energy at the second of said portions producin second magnetic field components in said region also predominantly of a single polarization, said first and said second components intersecting in said region at an angle a where oc=(2lt+ 1 )1r-;8, n being an integer, to produce circular polarization in said element, and means for magnetically polarizing said element in a direction perpendicular to said intersecting components.

6. The combination according to claim 5 wherein said portions are a quarter wavelength apart at said given frequency and wherein said first and said second field components intersect at right angles.

7. The combination according to claim 5 wherein said gyromagnetic material is biased to gyromagnetic resonance.

8. The combination according to claim 5 wherein the coupling between said portions and said element is in the region of critical coupling to produce nonreciprocal attenuation.

9. The combination according to claim 5 wherein the coupling between said element and said portions is greater than critical coupling to produce low-loss nonreciprocal phase shift eifects.

10. In an electromagnetic wave system supportive of wave energy .in the TEM mode at a given frequency, an isolator comprising first and second series connected sections of two-conductor transmission line each tuned to resonance at said given frequency and spatially oriented to cross each other at right angles in a region along each of said sections wherein the current is a maximum, an element of gyromagnetic material disposed in said region, means for magnetically biasing said material to gyromagnetic resonance at said frequency, an input circuit coupled to one end of said first section, means for producing a ninety degree phase delay in said wave energy coupled between the other end of said first section and one end of said second section, and an output circuit coupled to the other end of said second section.

11. A nonreciprocal wave transmission device supportive of wave energy in the TEM mode at a given frequency comprising a section of transmission line having first and second conductively insulated metallic members each tuned to resonance at said given frequency and spatially oriented to cross each other at a point along their respective lengths at which the current in each is a maximum, an element of gyromagnetic material disposed between said members at said crossover point, means for magnetically biasing said material to gyromagnetic resonance at said given frequency, means for coupling an input circuit to one end of said first member defining a first reactive impedance, means for coupling the other end of said first member to one end of said second mem- 12 her delayed in time, and means coupled to the other end of said second member to an output circuit defining a second reactive impedance.

12. The combination according to claim 11 wherein said means for coupling the other end of said first member to said one end of said second member comprises a third conductively insulated metallic member disposed between and electromagnetically coupled to said first and said second members.

13. The combination according to claim 12 wherein said electromagnetic coupling between said third and said first members defines a third reactive impedance, and wherein said electromagnetic coupling between said third and said second member defines a fourth reactive impedance.

14. The combination according to claim 13 wherein said third member has an electrical length at equal to 11' 1 2 2 (2m+1) [arctan -l-arctan wherein m is an integer and X and X; are said third and fourth reactive impedances, respectively.

15. The combination according to claim 13 wherein said first member has an electrical length 0 equal to wherein n is an integer and X and X are said first and said third reactive impedances, respectively.

16'. The combination according to claim 13 wherein said second member has an electrical length 0 equal to wherein n is an integer and X and X; are said second and said fourth reactive impedances, respectively.

17. A nonreciprocal wave transmission component comprising a pair of serially connected resonant sections supportive of electromagnetic wave energy at a given frequency, said energy as supported in each of said sections having a standing wave magnetic field pattern, said sections oriented with components of the magnetic field pattern of the first of said sections intersecting at right angles components of the magnetic field pattern of the second of said sections, a magnetically polarized element of gyromagnetic material disposed in the region of said intersecting magnetic field components, means for coupling electromagnetic wave energy into said first section defining a first reactive impedance X means for coupling said wave energy out of said first section into said second section ninety degrees delayed in time defining a second reactive impedance X and means for coupling said wave energy out of said second section defining a third reactive impedance X wherein X =X X 18. In an electromagnetic wave system, means for producing nonreciprocal wave transmission comprising a twoelement transmission line, means for supporting said elements in fixed spaced relationship with respect to each other comprising a low-loss dielectric material disposed therebetween, at least one of said elements comprising a plurality of conductively insulated sections extending in longitudinal succession with adjacent ends of said sections spaced apart to form gaps in the conductive continuity of said one element, the first of said sections and the last of said sections crossing each other at a given angle at a point substantially midway along their respective lengths, an element of gyromagnetic material located between said sections at their point of crossing, and means for magnetically biasing said element.

19. A nonreciprocal electromagnetic wave device comprising a section of transmission line having an input end and an output end, means for applying wave energy at a given frequency to the input end of said line, said wave energy propagating from said input end toward said output line, means for coupling wave energy exclusively between said two distinct portions of said line and said element said coupling means being supportive. of magnetic field components with the wave energy at the firstof said portions inducing first magnetic field components in said rea gion predominantly of a single polarization and with the waveenergy at the second of said portions inducing second magnetic field components in said region also predominantly of a single polarization, said first and said second components intersecting in said region at an angle on Where a: (2n+1')'1r, n being an integer, to produce circular polarization in said element, andmeans for mag- 14 netica'lly polarizing said element in a direction perpendicular to saidintersecting components.

20. A nonreciprocal wave transmission component comprising a section of hollow, conductively bounded waveguide form-ing a loop having an electrical length ,8 between respective ends, said section crossing over itself at an angle a Where on: (2n+1)1rB, n being an integer, an element of magnetically polarizable material exhibiting gyrorna-gnetic etfects over the operating frequency range of said component located between said ends of said loop at said" crossover region and extending into said guide at both of said ends through apertures in the Wall of said guide, and means for biasing said element in a direction substantially normal to the plane of said loop.

No references cited. 

1. A NONRECIPROCAL WAVE TRANSMISSION COMPONENT COMPRISING A TWO-CONDUCTOR TRANSMISSION LINE, AT LEAST ONE OF SAID CONDUCTORS FORMING A LOOP OF ELECTRICAL LENGTH B, SAID ONE CONDUCTOR CROSSING ITSELF AT AN ANGLE A, SUCH THAT A=(2N+1)$-B, N BEING AN INTEGER, AN ELEMENT OF MAGNETICALLY POLARIZABLE MATERIAL EXHIBITING GYROMAGNETIC EFFECTS OVER THE OPERATING FREQUENCY RANGE OF SAID COM- 